Microcontrollers, microprocessors and other devices used to control integrated circuit devices can be used in many different types of electronic equipment. In many such applications, such devices have a typical usage profile of a very short program execution time (e.g., some microseconds) followed by a transition to a low power mode. In integrated circuits, particularly when used in portable electronic devices, a primary goal is always to save power, so that the batteries used to supply power can maintain a long life.
In many microcontrollers and microprocessors, the digital core and other parts of the device may be supplied with power via a low dropout (LDO) voltage regulator. Such regulator is a linear voltage regulator that regulates the primary supply voltage to provide a stable supply voltage with little voltage drop. However, the LDO regulator itself consumes power; thus, it is desirable to switch the regulator itself off or place it in a low power condition when the microcontroller or other device to be powered is not active. Because the microcontroller or other powered device is sometimes switched on only for a relatively short period of time, this means that the LDO regulator must be switched on and off very quickly. Unfortunately, an LDO regulator designed to achieve quick switching (i.e., switching it on and off, or enabling and disabling it) consumes a large amount of power. In addition, such LDO regulator circuits have long settling times and therefore take a long time to settle after being enabled—typically much longer than the program execution time of a microcontroller or the like. Since the output voltage of the regulator is not able to settle during a relatively short active time, this might lead to unpredictable and incorrect LDO regulator output voltages. Thus, a trade-off is generally required between the switching capability, i.e., the settling time, and the power consumption of an LDO regulator.
Some conventional solutions utilize a window comparator to reduce error in the output voltage of an LDO regulator. The comparator is coupled to the regulator output and continuously monitors the output voltage. If the output voltage goes outside a given tolerance range, then the output voltage is corrected by feeding a current to the corresponding node. The window comparator, however, requires additional circuitry and also some reference voltages. Moreover, the window comparator cannot be switched off during inactive times. Accordingly, the power consumption and chip area requirements are increased.